The field of the invention is chemical analysis of water solutions, liquids or gas analysis, and the invention relates more particularly to the use of multiple electrodes on a single probe so that several readings may be made at a single immersion.
Electrode measurements in solution can be grouped into two general classes, namely, active measurements and passive measurements. Passive measurements are those in which the measurement process does not perturb the solution. Examples of passive measurements include the measurement of temperature, pH, the measurement of the reference potential of a solution and the measurement of an ion selective electrode potential. Active measurements result in some external perturbation of the solution to carry out the measurement. This is generally applied by some portion of the measurement sensor. Examples of active measurements include the measurement of conductivity, the measurement of dissolved oxygen and the measurement of dissolved carbon dioxide.
The use of combination electrodes such as pH and reference potential or oxidation reduction potential and reference potential has long been known to simplify design problems. These combination electrodes ease cabling problems and reduce the amount of sample required for a measurement. In the past, combination electrodes have either been exclusively passive sensors or have been used to measure only a single parameter at a time. It was believed that the interference of the reading of one sensor by the operation of another precluded the grouping of such interfering sensors.